Slabs manufactured by a continuous casting process are molded, cut into pieces with an appropriate length, heated in a reheating furnace, and then inserted into a rolling mill, thereby manufacturing hot rolled coils. However, slabs manufactured by the continuous casting process generally have corner cracks in corner areas. Particularly, a steel of a grade such as medium carbon steel having peritectic transformation has serious corner cracks.
Corner cracks of slabs may cause manufacturing accidents such as fractures of panels during a rolling process and may cause defects such as edge scabs in manufactured hot rolled coils to require cutting out a considerable amount of corner portions of hot rolled coils. Accordingly, slabs of a steel grade which easily have corner cracks therein have been scarfed to remove corner portions before a rolling process. Also, since sharp corners of slabs intensively wear and tear particular portions of a rolling mill during a rolling process and shorten a life of the rolling mill, it is necessary to scarf corners of slabs also to protect the rolling mill.
Hitherto, scarfing operation was performed by scarfing corner portions of a slab while a worker directly carried a scarfing nozzle like an example disclosed in U.S. Pat. No. 3,254,696. However, in this way, since a worker must work in a poor environment while wearing heat proof clothes, intensity of work is very high, there is a risk of safety accidents, and because it is difficult to stably maintain a scarfing nozzle during a working process, scarfed surfaces are uneven.
To improve this, Korean Patent Publication No. 10-2012-0001823 discloses a method of embodying a fast and stable scarfing by scarfing corner portions of a slab using a torch type cutting device while the slab is being transferred.
Meanwhile, it is necessary for scarfing to change a scarfing shape of corner portions according to the steel grade of a slab, temperature, and scarfing speed. However, the conventional scarfing device has an inconvenience associated with having to replace the whole scarfing nozzle to change the scarfing shape. Also, when a thickness of a slab to be scarfed changes, it is necessary to replace a nozzle or adjust a position of the nozzle again.